A potential network of permanent forest plots for the West Coast Conservancy P J Bellingham Landcare Research PO Box 69 Lincoln Published by Department of Conservation Head Office, PO Box 10-420 Wellington, New Zealand This report was commissioned by the West Coast Conservancy ISSN 1171-9834 1998 Department of Conservation, P.O. Box 10-420, Wellington, New Zealand Reference to material in this report should be cited thus: Bellingham, P. J. 1998 A potential network of permanent forest plots for the West Coast Conservancy. Conservation Advisory Science Notes No. 188. Department of Conservation, Wellington. Keywords: forest measurement, indigenous forests, biodiversity, sustainable management, carbon budgets, West Coast Conservancy, National Vegetation Survey Abstract Permanent plots in indigenous forests administered by the Department of Conservation's West Coast Conservancy in the National Vegetation Survey (NVS) database were analysed to show which forest types were adequately sampled according to identifiable forest types, and within each type, in space and in time. From 404 permanent forest plots considered in analysis, eight forest types were determined, of which only one (southern rata - kamahi - Hall's totara) is adequately represented in total number of plots and in meas- urements over time. Even this type is inadequately represented in space. Permanent plot coverage in Westland is overall very patchy, with the Whitcombe Ecological District having more than half the total number of permanent forest plots. There are no permanent forest plots in the NVS data- base in most Ecological Districts in the West Coast Conservancy, and cover- age of major protected natural areas is often either scant (e.g., in Paparoa National Park), or absent entirely (the West Coast Conservancy parts of Kahurangi National Park). This report recommends a network of 287 plots to be retained for long-term monitoring of forest condition and trend. Good long-term data sets exist from some plots (3 and rarely 4 measurements), and these plots should be accorded high priority for ongoing measurement. How- ever, given the patchy coverage of plots, it is strongly recommended that other sources of permanent plot data outside NVS (e.g., from Crown Research Insti- tutes and Universities) and from other administrators of indigenous forests (especially Timberlands West Coast Limited) be integrated with NVS plots so that a more complete and widespread assessment of forests can be obtained. 1. Introduction New Zealand's recent international obligations under a range of international conventions require better knowledge about biodiversity within indigenous forests, and about changes in forest condition and composition over time. Most notably, New Zealand has obligations to report on: biodiversity under the Convention on Biodiversity; sustainable management of forests (including their biodiversity) under the Global Forest Resource Assessment 2000 and the Montreal Process; national carbon budgets under the Framework Convention on Climate Change. In forests administered by the Department of Conservation (DoC), regional and national operations, for example against animal pests, require reporting under the philosophy of Quality Conservation Management. New Zealand's existing network of permanent forest plots has enabled deter- mination of several aspects of forest ecology, including change over time, and 1 can be used in future for a variety of purposes. Permanent plots have pro- vided information on national estimates of carbon (Hall & Hollinger 1997), long-term forest condition and mortality patterns (e.g., Bellingham et al. 1996), changes in seedling regeneration over time (e.g., Stewart & Burrows 1989), changes in biodiversity over time (e.g., Stewart et al. 1987), and exotic inva- sions over time (Wiser et al., in revision). Permanent forest plots can therefore provide information on regional and national changes in forest condition using the following as indicators: tree death (and defoliation) by species as an indicator of forest health; regeneration by species as an indicator of forest maintenance; exotic plant species invasion as an indicator of intactness; browsing by introduced animals as an indicator of animal impacts; living and dead stem biomass as a habitat indicator; and rare and threatened plants as an indicator of maintenance of diver- sity. To assist the West Coast Conservancy of DoC in devising a network of perma- nent plots for ongoing assessment of changes in forest condition, an assess- ment of permanent plots in indigenous forests held in the National Vegeta- tion Survey (NVS) database was conducted by Landcare Research. Data from permanent plots were analysed so that various forest types were defined, and recommendations were made for a subset of the permanent plots to be main- tained for onward monitoring of forest condition and trends. Work was con- tracted in April 1997 and completed in July 1997. 2. Objective To recommend a network of permanent plots suitable for onward measure- ment to assess forest condition in indigenous forests administered by DoC's West Coast Conservancy. 3. Background 3.1 THE NATIONAL VEGETATION SURVEY Several thousand permanent sample plots have been established in New Zea- land in indigenous forests (Allen 1993). Many of these plots have been estab- lished using similar methods that allow comparisons among them in terms of 2 quantifying biomass and species composition. Repeated measurement of these plots allows assessments to be made of forest dynamics. The great majority of permanent plots in indigenous forests were established on the basis of two historic rationales: (a) to assess timber volumes or forest structure and composition (mostly in lowland forests); and (b) to assess the effects of introduced browsing mammals on forest condition, structure, and composition (mostly in upland 'protection' forests). The dictates of these two management needs have direct consequences for where the present network of plots is sited. Most plots established to determine timber volumes were focused on 'merchantable' stands, and thus were not necessarily representa- tive of the vegetation of an area. Moreover, as logging of indigenous forests declined, so the need to establish plots to determine timber volumes declined, and thus many of these plots are old (1940s to 1950s) and difficult to relo- cate. In contrast, most of the permanent plots established to determine the effects of browsing mammals are generally of more recent origin (1970s to 1980s). Since plot location was not dictated so much by a priori decisions about what vegetation was to be sampled, but more by the effects of brows- ing animals, the sampling effort tended to concentrate on where these ani- mals were most common, i.e., in steeper montane areas usually within large forest tracts. In the West Coast Conservancy, most forest plots in the National Vegetation Survey (NVS) database are from larger forested tracts. Most of these plots were established in the 1970s and most were designed to measure the effects of browsing mammals in indigenous forests. The complete set of data from permanent plots in forests administered by DoC in the West Coast Conserv- ancy was examined to determine: (a) where plots are located; (b) what kinds of forest vegetation the plots sample, and on that basis, how well sampled are particular types of forest; and (c) how frequently plots in particular areas and in particular kinds of for- est have been resampled, in order to assist in determining long-term trends within these forests. 4. Methods Data from permanent plots in forests administered by DoC West Coast Con- servancy usually have been collected after the methods of Allen (1993), i.e., from 20x20 m (400 plots, although a few plots are of other sizes. Within these plots all stems 22.5 cm diameter at breast height (dbh: 1.35 m) have been identified, permanently tagged with aluminium tags nailed at the point of diameter measure, and their diameters recorded. Each plot is normally subdivided into 16 contiguous 5x5 m (25 subplots, within which counts of saplings are made and within which seedling subplots are sited (see details 3 in Allen 1993). A standard forest reconnaissance survey plot (Allen 1992) usually accompanies each permanent plot, along with site data, typically a map reference, and estimates of altitude, slope, and aspect. The plots are normally semi-randomly located within catchments to be sur- veyed, i.e. at systematically assigned distances along transects following semi- random bearings from a base assigned randomly along major stream courses. A few of the plots were located on the basis of stratification of vegetation determined from aerial photographs. Data from each permanent plot are recorded in a standard format in the NVS database. In this exercise, only data from the trees (i.e. stems 22.5 cm dbh) were used, and the analysis program converted data for each species to a total basal area per hectare, to render plots of different size comparable. Where plots had been measured more than once, the most recent survey data were used. I did not use in the analysis data from 307 permanent 20 x 20 m plots estab- lished in the Taramakau and Otira catchments in 1987, of which 102 were remeasured in 1993, because in contrast to all other plots, only stems 210 cm dbh were tagged and recorded. Thus data from these plots were not compa- rable with those from other plots. Another data set in the NVS database omit- ted from analyses is 53 plots from Saltwater Forest. Because I have limited the focus of this study to forests administered by DoC, these data were excluded because they were collected on land administered by Timberlands West Coast Limited (hereafter Timberlands); moreover, the data were collected from trees 210 cm dbh and thus are not readily comparable with other data. All the most recent information collected from 404 permanent plots in the NVS database from the West Coast Conservancy were combined into a stand- ard format. Site information exists from each of the plots, typically its map grid reference (either NZMS 1 or NZMS 260), elevation, slope, and aspect.